The purpose of such stands is to hold a relatively heavy microscope for an operator so that it is movable with as little resistance as possible. The joints or bearings need to be made as resistance-free as possible so as to present the user with as little resistance as possible when moving the stand or the stand arms.
If these stands are positioned on uneven floors or if torques on the stand occur as a result of changes in loads, the relevant moving parts of the stand, in particular the stand arm, exhibit a drift behavior in the unbraked state. “Drift behavior” is to be understood as lateral pivoting motions about a rotation axis, or tendencies toward such pivoting motions, by the carrier arm, which are undesirable for the user.
Drift can occur with ceiling mounts as well. It results whenever deflections occur as a result of limited rigidity of one of the horizontal stand arms, and further horizontally arranged arms or components are pivotably mounted on that stand arm.
In surgical microscopes, drifting of the stand arms about an axis is prevented by way of an electromagnetic brake. When this brake is released, however, in order to displace the stand or the microscope arranged on the stand, the moving parts of the stand can drift and the operator must exert a corresponding amount of force in order to stop that drift.
A stand for a surgical microscope having an electromagnetic brake is known from DE 101 23 166 A1. In order to optimize drift behavior when the brake is released, provision is made in the context of this stand for each individual pivot axis automatically to be held perpendicular by way of a complex mechanism. This mechanism has proven successful in practice, but its production is complex and correspondingly expensive. Especially in the case of stands for surgical microscopes which, because of their utilization, are pivoted over only very small ranges (as is the case, for example, with stands for ophthalmology), lesser requirements are imposed in terms of absence of drift in the stand.